Optical system for ophthalmological instruments

ABSTRACT

A compactly designable optical system for ophthalmological instruments comprising an illumination system so adapted as to illuminate a fundus with rays having passed through a ring slit and been focused on the cornea of an eyeball to be examined, and an observation/photographing system so adapted as to permit observing and photographing an image of said eyeball with a small reflector mirror arranged in said illumination system so as to be inclined with regard to the optical axis thereof and a relay lens for focusing the rays which are reflected by the fundus, passing through said objective lens and reflected by said small reflector mirror.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an improvement of an optical system forophthalmological instruments such as fundus cameras.

(b) Field of the Invention

The conventional fundus camera has such a composition as shown in FIG. 1wherein the reference numeral 1 represents an eyeball to be examined,the reference numeral 2 designates an objective lens, the referencenumeral 3 denotes a mirror having an aperture, the reference numeral 4represents a stop, the reference numeral 5 designates a relay lens, thereference numeral 6 denotes a switching mirror, the reference numeral 7represents an eyepiece, the reference numeral 8 designates a filmsurface, the reference numeral 9 denotes a light source for observation,the reference numeral 10 represents a heat-preventive filter, thereference numeral 11 designates a photographing light source such asstrobo tube, the reference numeral 12 denotes a ring slit, referencenumerals 13 and 14 represent collector lenses, and the reference numeral15 designates a lens for projecting an image of the ring slit. In thisoptical system, the light source 9 is always lit and emits rays whichare focused by the collector lens 13 so as to form an image of the lightsource 9 at a position substantially the same as that of thephotographing light source 11. This image of the light source is focusedagain by the collector lens 14 at a position in the vicinity of the ringslit 12. Therefore, the ring slit functions as a secondary light sourcein the optical system arranged at the subsequent stage. The rays havingpassed through this ring slit are projected by the projector lens 15 toa position in the vicinity of the mirror 3 having an aperture. Thisimage of the ring slit is further projected by the objective lens 2 tothe cornea surface of the eyeball to be examined to achieve ring-shapedillumination already known to those skilled in the art. The illuminatingrays scattered by the fundus illuminated in this way are projectedthrough the cornea and focused by the objective lens 2 so as to form animage of the fundus at a position between the objective lens 2 andmirror 3 having an aperture. This image of the fundus is passed throughthe stop 4, focused by the relay lens 5 and reflected by the switchingreflector mirror 7 and reflector mirror 7a, and formed again on afocusing plate 7b for observation through the eyepiece 7c. When theswitching mirror 6 is turned to the position indicated by the chainline, the image of the fundus is formed on the film surface 8 forphotographing.

In order to design a fundus camera comprising such an optical systemmore compact, there can be considered a method to design the lenses morecompact, another method to shorten the total length of the lens systemas a whole, a third method to shorten focal length of the lens system asa whole and so on. However, all of these methods offers possibility todesign the optical system compactly only within a certain limited range.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical system forophthalmological instruments which comprises a small reflector mirrorand can be designed compact.

A further object of the present invention is to provide an opticalsystem for ophthalmological instruments comprising an illuminationsystem so adapted as to illuminate fundus of an eyeball to be examinedwith illumination rays having passed through a ring slit and anobjective lens, and an observation/photographing system so adapted as topermit observing and photographing an image of the fundus of saideyeball to be examined with a small reflector mirror arranged in saidillumination system so as to be inclined with regard to the optical axisthereof and a relay lens for focusing the rays reflected by the fundus,passing through said objective lens and reflected by said smallreflector mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view illustrating the composition of theoptical system for the conventional fundus camera;

FIG. 2 shows a sectional view illustrating composition of the opticalsystem for fundus camera according to the present invention; and

FIG. 3 shows a perspective view of an optical element which serves bothas a small reflector mirror and a ring slit to be used in the opticalsystem according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, the optical system for ophthalmological instruments according tothe present invention will be described more detailedly with referenceto a preferred embodiment shown in the accompanying drawings.

In FIG. 2, the reference numeral 21 represents an eyeball to beexamined, the reference numeral 22 designates an objective lens, thereference numeral 23 denotes a ring slit, the reference numeral 24represents an optical element having a small reflecting surface soconstructed as to be described later, the reference numeral 25designates a relay lens, the reference numeral 26 denotes a switchingmirror, the reference numeral 27 represents a reflector mirror, thereference numeral 28 designates a focusing plate, the reference numeral29 denotes an eyepiece and the reference numeral 30 represents a filmsurface. In addition, the reference numeral 31 designates a light sourcefor observation, the reference numeral 32 denotes a heat-preventivefilter, the reference numeral 33 represents a light source forphotographing such as a strobo tube, and the reference numerals 34 and35 designate collector lenses respectively.

The optical element 24 used in the optical system shown in FIG. 2 ismade of a transparent disc 24a at the center of which is formed aprotrusion 24b having a reflecting surface slanted toward the objectivelens.

In the optical system comprising such an optical element 24 shown inFIG. 2, the rays emitted from the light source 31 pass through thetransparent disc 24a and are focused to form an image of the lightsource in the vicinity of the ring slit 23 in the same manner as that inthe conventional optical system shown in FIG. 1. The rays having passedthrough the ring slit 23 are focused by the objective lens 22 so as toform an image in the vicinity of the cornea for illuminating the fundusof the eyeball to be examined.

A ring-shaped illumination is achieved in this way. Subsequently, therays scattered by the fundus pass through the objective lens 22 and arereflected on the small reflecting surface of the protrusion 24b,thereafter passing through the relay lens 25 and being used forobservation or photographing in the same manner as that in theconventional optical system shown in FIG. 1.

Since the ring slit 23 and the cornea of the eyeball to be examined arekept in a conjugate relationship with regard to the objective lens 22 inthe optical system based on the ring illumination method according tothe present invention described above, the rays reflected by the corneareturn to the circular aperture of the ring slit. Therefore, the raysreflected by the cornea surface are not reflected by the smallreflecting surface of the optical element 24 and do not enter thephotographing/observation system. Since the small reflecting surfacefunctions to separate and select the image of the fundus from the raysreflected by the cornea surface so as to make the former to follow adifferent optical path, the image of the fundus formed on the filmsurface or the focusing plate is free from flare.

Since the optical system according to the present invention adopts asmall reflector mirror instead of the mirror having an aperture toseparate the illumination system from the photographing/observationsystem as described above, the illumination system is laid out linearly.

Though it may seem that a simple small reflector mirror inclined withregard to the optical axis of the objective lens 22 can be used in placeof the optical element having the above-described construction, thelatter is more convenient when a fixing mean for it is taken intoconsideration.

FIG. 3 shows a different example of the optical element 24 having asmall reflecting surface which is made of a transparent disc 40 such asa glass disc having a central portion 40a, a circumferential portion 40bwhich are painted black or bonded to light-shielding plates so as toform light-shielding portions, and a ring-like transparent portion 40creserved therebetween so as to serve as a ring slit. Arranged on thecentral light-shielding portion 40a is a protrusion 41 having a topreflecting surface so slanted with regard to the optical axis as to forma reflecting surface 41a.

The optical system according to the present invention permitsring-shaped illumination and observation of fundus without using theconventional reflector mirror having an aperture. As a result, saidoptical system is so adapted so as to allow the objective lens to forman image of the ring slit on the cornea surface of the eyeball to beexamined without forming it in the vicinity of the reflector mirrorhaving an aperture. Said optical system therefore requires no lens whichfunctions to project an image of the ring slit to the vicinity of thereflector mirror having an aperture. Further, the optical element 24 canhave the function described below when it has the centrallight-shielding portion larger than the reflecting surface. When animage of the ring slit is formed on the cornea surface with theobjective lens, the image quality is apt to be degraded due toaberrations produced by the objective lens. Further, position of theeyeball to be examined may deviate from the position perfectly conjugatewith the ring slit. Moreover, the rays reflected by the cornea surfaceare subjected to influence due to aberrations produced by the objectivelens. Due to these influences, the image of fundus cannot be separatedand selected completely from detrimental rays by the small reflectingsurface only. When the central light-shielding portion is larger thanthe reflecting surface and forms a dead zone which does not transmitneither the rays reflected by the fundus or the illumination raysbetween the sections forming the paths for both the kinds of rays, theoptical element can completely separate both the types of rays to makethe image of fundus free from flare, etc. even when its quality isdegraded a little. The optical element 24 can therefore eliminate thenecessity of the stop 4 used in the optical system shown in FIG. 1.

As is understood from the foregoing descriptions, the optical systemaccording to the present invention makes it possible to arrange a smallreflecting surface in place of the mirror having an aperture used in theconventional fundus camera and place a ring slit directly in thevicinity of said reflecting surface. Said optical system thereforeeliminates the necessity of the space which was conventionally requiredto project an image of the ring slit to the vicinity of the mirrorhaving an aperture by using a projector lens, thereby making it possibleto design the optical system more compact or simplify the compositionthereof. In addition, the optical system uses no projector lens andeliminates the problem of deformation of image due to aberrationsproduced by a projector lens, thereby assuring optical characteristicmore excellent than that of the conventional optical system.

What is claimed is:
 1. An optical system for ophthalmologicalinstruments comprising an illumination system comprising a light source,collector lenses, a ring slit having a central light shielding portionarranged in close proximity an image of said light source formed withsaid collector lenses and an objective lens so arranged as to form animage of said ring slit in close proximity to the cornea of an eyeballto be examined, and a photographing/observation system comprising saidobjective lens, a small reflector mirror arranged in close proximity tosaid ring slit and positioned on and inclined with regard to the opticalaxis of said objective lens and a relay lens for focusing the raysreflected from the fundus of the eyeball to the examined after said rayshave passed through said objective lens and been reflected by said smallreflecting mirror.
 2. An optical system for ophthalmological instrumentsaccording to claim 1 wherein said small reflector mirror has a diametersmaller than that of the central light-shielding portion of said ringslit.
 3. An optical system for ophthalmological instruments according toclaim 1 wherein said small reflector mirror consists of a transparentplate and a protrusion protruding from said transparent plate and havinga reflecting surface.
 4. An optical system for ophthalmologicalinstruments according to claim 1 wherein said ring slit and said smallreflector mirror are composed as a member consisting of a transparentplate forming light-shielding portions while leaving a ring-liketransparent portion and a protrusion protruding from said transparentplate and having a reflecting surface.